Various techniques for measurement of properties of thin film layers are known in the art. These techniques have become important particularly (though not exclusively) in the field of semiconductor device manufacturing, in which microcircuits are built up from thin film elements on the surface of a semiconductor wafer.
Some measurement techniques use various types of X-ray scattering. The term “scattering” is used broadly in the present patent application to refer to any and all processes by which X-ray irradiation of a sample causes X-rays to be emitted from the sample. Thus, in this context, “scattering” includes the techniques of X-ray reflectometry (XRR), X-ray diffraction (XRD), X-ray fluorescence (XRF), and small-angle (grazing-incidence) X-ray scattering (SAXS), for example. Systems and methods for thin film measurement using these various types of X-ray scattering are described, for example, in U.S. Pat. Nos. 6,639,968, 7,551,719, and 7,804,934, whose disclosures are incorporated herein by reference.
Other measurement techniques use vacuum ultraviolet (VUV) optical metrology, based typically on reflectometry and/or ellipsometry. The terms “vacuum ultraviolet” and “VUV” as used in the present patent application refer to radiation in the spectral region below 190 nm. Systems and methods for thin film metrology using VUV reflectometry are described, for example, in U.S. Pat. Nos. 7,026,626 and 7,126,131, whose disclosures are incorporated herein by reference.